There has been known acoustic wave devices such as SAW (Surface Acoustic Wave) devices and piezoelectric thin film resonator devices as filters and duplexers having an excellent high-frequency characteristic. Since high-frequency signals are used in the acoustic wave device, a parasitic capacitor formed by a terminal and a line pattern included in the acoustic wave device may cause deterioration in a frequency characteristic of the acoustic wave device. There is disclosed an invention that provides the line pattern on an insulating layer in Japanese Patent Application Publication No. 2004-282707 (Patent Document 1). There is disclosed an invention that provides the line pattern and the ground terminal on an insulating layer in Japanese Patent Application Publication No. 2004-88551 (Patent Document 2).
However, the techniques disclosed in Patent Documents 1 and 2 do not reduce the parasitic capacitance sufficiently. For example, when the substrate is made to be thin to reduce the height of the acoustic wave device, the parasitic capacitance between the front surface and back surface of the substrate increases.